This invention relates to an improved resin composition and more particularly to an improved styrene/butyl acrylate resin composition useful for making electrostatographic toner compositions.
Styrene/n-butyl acrylate resins are known in the art.
For example, U.S. Pat. No. 5,102,764 discloses a styrene/n-butyl acrylate polymer resin with a magenta dye dispersed in the polymer resin. The resin is disclosed as having a glass transition temperature in the range of from about 40.degree. C. to about 90.degree. C. and a molecular weight range of 50,000 to 250,000. As a further example, U.S. Pat. No. 5,064,739 discloses a magnetic developer consisting of a magnetic carrier and a magnetic toner. The toner comprises, for example, a styrene/n-butyl acrylate copolymer with Mn=30,000 and Mw=200,000.
Styrene/n-butyl acrylate polymer toners of similar chemical composition to toners of the present invention are known. For example, Nippon Carbide manufactures a toner, identified as NCHT041C, which is 88% styrene and 12% n-butyl acrylate. The toner has molecular weight properties of Mn=3,336, Mw=19,776 and MWD=5.93 and a glass transition temperature of 65.8.degree. C. Although the toner has good gloss properties, with gloss temperatures between 139.degree. C. and 148.degree. C., it has poor fix properties, with a fixing fusing temperature of 176.degree. C. This emulsion/aggregation toner is included and analyzed as a Comparative Example, below.
Experimentation in the art of toner resin production has focused upon narrow molecular weight regions with narrow molecular weight distributions, as those two variables greatly affect the gloss and fix properties of the resins. In many cases a trade-off is necessary between the gloss and fix properties of the toner, and such a trade-off usually results in an increase in the fusing temperature (which is defined as the temperature at which the toner will fuse onto the paper to give the desired property). For example, a toner designed with high gloss properties often has poor fix behavior. Either the toner is too brittle and has poor mechanical properties or the particles are not well coalesced to each other and thus do not adhere well to the paper. In other cases, the fix properties of the toner may be very good, but only at the expense of the gloss properties. Efforts to improve both the gloss and the fix properties of toner resins have been undertaken, but have met minimal success.
As described herein, the gloss and fix properties of a styrene/n-butyl acrylate resin are both related to the molecular weight properties of the resin, but in an opposite manner. As the molecular weight increases, the fix properties of the resin increase proved the glass transition temperature (Tg) of the resin remains constant. In addition, the gloss properties of the resin decrease as the molecular weight increases. For this reason, it was believed within the toner/developer community that a styrene-acrylate based resin could never produce glossy images of the same level as conventional polyester-based toners. The resins of the present invention overcome this misconception.